1. Field of the Invention
The invention relates to highly concentrated oil-in-water emulsions of Si-, O-, C- and H-containing organopolysiloxanes which furthermore contain the elements N and/or S, having a pH of at least 7.5, and a process for the preparation of emulsions having a narrow particle size distribution.
2. Description of the Related Art
Silicone emulsions have been prepared and traded for decades in large quantities.
Emulsions are disperse systems of two or more liquids immiscible with one another. Known classes of emulsions are the microemulsions and macroemulsions, a distinction also being made between oil-in-water and water-in-oil emulsions.
In accordance with the prior art, water-immiscible substances, e.g. silicone oils, together with one or more emulsifiers, are stably dispersed into small droplets in water. A preservative and further additives are optionally added to the emulsion.
Highly concentrated emulsions, i.e. emulsions which contain more than 40% of siloxane, are often water-in-oil emulsions (W/O-emulsions). These W/O-emulsions are, however, not water-dilutable and therefore not suitable for industrial applications. Highly concentrated oil-in-water emulsions which can be immediately further diluted with water are desirable.
It is known that, particularly in the case of amino-functional siloxane emulsions, addition of acid or partial conversion of the amino groups into ammonium ions, considerably improves the stability of the emulsion or, in the case of many emulsions, is absolutely essential for obtaining a shelf life sufficient for sale. This applies in particular when relatively high temperatures in the range of 35-50° C. may occur during storage. Furthermore, the pH of the emulsion is also important for problem-free use. The known aminosiloxane emulsions become unstable at a pH >7 and silicone oil separates, which leads to undesired silicone spots on textiles treated with such emulsions. This is disclosed, for example, in DE 196 52 524 A1 and DE 100 04 321 A1.
A consequence of this is evident not least from the fact that, in the case of virtually all siloxane emulsions sold on the market, at least some of the amino groups present have been converted with acid into ammonium groups.
For example, EP 417 047 A, EP 459 821 and EP 404 027 describe microemulsions or macroemulsions of aminosiloxanes, wherein acid, and optionally further stabilizing additives are always employed. Furthermore, emulsions of aminosiloxane are known wherein the aminosiloxane is present partly in salt form, an indirect indication of the concomitant use of acid. Aminosiloxanes which have been partly converted into salt form are described, for example, in DE 4 004 946, it being clearly evident from the working examples that acid is used.
Emulsions of nitrogen-containing siloxanes which are prepared without acid but with a low siloxane content in the emulsion are described, for example, in DE 3 842 471; this is an amidosiloxane microemulsion having a siloxane content of 15%.
Although reduced transportation and storage costs argue in favor of the use of emulsions which are as concentrated as possible, the solids content of siloxane macroemulsions sold on the market is typically substantially less than 50%. This is due to the fact that although more highly concentrated siloxane emulsions can be prepared using existing techniques, they have such a high viscosity or typically exhibit such an increase in the viscosity during storage that they are not suitable for the majority of applications, which require good flowability and easy dilutability without complicated technical aids.
That highly concentrated emulsions are often very highly viscous and are therefore virtually impossible to handle is disclosed in DE 198 35 227 A1.
It is therefore of interest to prepare highly concentrated, low viscosity emulsions without the use of additives. Furthermore, it is of particular interest to provide highly concentrated, low-viscosity, stable emulsions which contain only a small proportion of emulsifier.